As vehicle helmets worn by the rider of a motor cycle or the like, a full-face-type helmet and a jet-type helmet are conventionally known. In the full-face-type helmet, a chin cover for covering the chin of the helmet wearer is integrally formed with the head protecting body. In the jet-type helmet, no chin cover is formed on the head protecting body so as to expose the face of the helmet wearer almost entirely. Another full-face-type helmet (to be referred to as a "full-face-type helmet serving also as a jet-type helmet" hereinafter) is also conventionally known. In this full-face-type helmet, the head protecting body is formed of a main cap portion having almost the same shape as that of the head protecting body of a jet-type helmet, and a subsidiary cap portion attached to the main cap portion to be substantially vertically pivotal so as to selectively cover the chin of the helmet wearer, so that the helmet can have the functions of both a full-face-type helmet and a jet-type helmet.
In the conventional full-face-type helmet serving also as the jet-type helmet, when the subsidiary cap portion is at the lower position, it serves as a chin covering means. When the subsidiary cap portion is at the upper position, a large window formed in the main cap portion is opened, and the head protecting body accordingly has no chin covering means, in the same manner as in the jet-type helmet. When the wearer wearing the full-face-type helmet serving also as the jet-type helmet is driving a motor cycle at high speed, the helmet is worn with its subsidiary cap portion being lowered to the lower position, in order to prevent a large wind pressure from acting on the wearer's chin and its vicinity. The helmet is provided with a subsidiary cap portion locking mechanism for locking the subsidiary cap portion at the lower position with respect to the main cap portion, so that the subsidiary cap portion does not undesirably move upward by a large impact or wind pressure during high-speed driving. The subsidiary cap portion is provided with an unlocking means or member in order to unlock the subsidiary cap portion locked at the lower position by the subsidiary cap portion locking mechanism.
Such a conventional full-face-type helmet serving also as the jet-type helmet is disclosed in European Patent No. 518,178 as well. In the helmet disclosed in this reference (to be referred to as "the first known helmet" hereinafter), when a release lever serving as the unlocking member is pressed for unlocking, a force which moves the subsidiary cap portion from the lower position to the upper position automatically acts on the subsidiary cap portion. In other words, when the release lever is pressed upward, the subsidiary cap portion locked at the lower position is unlocked. Therefore, when the release lever is pressed upward to unlock the locked subsidiary cap portion, the subsidiary cap portion locked by the locking mechanism is unlocked. Also, the subsidiary cap portion can be started to move from the lower position to the upper position by only successively pressing the release lever. Hence, the wearer can unlock the locked subsidiary cap portion and move the unlocked subsidiary cap portion upward quickly and continuously by only pressing the release lever.
In the first known helmet as described above, assume that, while the wearer drives the motor cycle at high speed, for example, he erroneously presses the release lever upward so as to slightly move a shield plate (attached to the subsidiary cap portion to be able to open/close the window opening formed in the front surface of the head protecting body of the helmet), so that the window opening closed by the shield plate may be slightly opened. Alternatively, assume that a foreign matter accidentally abuts against the release lever from below. Then, the subsidiary cap portion locked at the lower position is unlocked, and undesirably moves upward from the lower position for a certain degree. A large wind pressure then can directly act on the wearer's chin, causing inconveniences for the wearer in driving the motor cycle.
In the first known helmet as described above, when an operation lever connected to the release lever through a wire causes a movable locking member made of a spring member to move forward against the spring force, the locking mechanism is unlocked. In spite that the structure of the mechanism for unlocking the subsidiary cap portion locked by the locking mechanism is not very simple, the subsidiary cap portion might not be unlocked or inversely locked by the locking mechanism quickly and smoothly.
The conventional full-face-type helmet serving also as the jet-type helmet, as described above, is disclosed in German Patent Laid-Open No. 19,612,724 as well. In the helmet (to be referred to as "the second known helmet" hereinafter) disclosed in this reference, when the release tap serving as the unlocking means is pressed for unlocking, a force opposite to a force that moves the subsidiary cap portion from the lower position to the upper position acts on the subsidiary cap portion. In other words, when the release tap is pressed downward, the subsidiary cap portion locked at the lower position is unlocked. Even when the release tap is continuously pressed, it is not sufficient to move the subsidiary cap portion from the lower position to the upper position. Therefore, when the wearer is driving the motor cycle at high speed, the subsidiary cap portion does not move upward from the lower position erroneously or accidentally, and accordingly large wind pressure will not substantially, directly act on the helmet wearer's chin.
In the second known helmet as described above, the movable locking member is constituted by an arcuated operation lever formed with the release tap at its central portion. The operation lever is pivotally, axially supported on the auxiliary cap portion at the right and left portions. Also, a pair of right and left engaging recesses are formed in the right and left end portions of the operation lever. When a pair of right and left lock pins provided to the main cap portion relatively engage with these engaging recesses, the subsidiary cap portion is locked on the main cap portion. When the helmet wearer holds the release tap with his fingers and moves it downward, the operation lever pivots forward to disengage the lock pins relatively from the engaging recesses, thereby unlocking the locked subsidiary cap portion. Therefore, in the second known helmet as well, in spite that the structure of the mechanism for unlocking the subsidiary cap portion locked by the locking mechanism is not very simple, the subsidiary cap portion might not be unlocked or inversely locked by the locking mechanism quickly and smoothly.